Winter Forecast/Pattern Update and Checkpoint
For reference, please access our 2018-2019 Winter Forecast issued in November right here.
Good morning y'all. Happy Monday, and I hope you all have enjoyed a wonderful weekend. This time of year always seems to pass us by so quickly; the holidays certainly add to the speed of which time seems to pass. Before we know it, it will be January and we will be buried in s....actually, let me digress for a moment. If you really take a moment to think about it, it feels like this "Winter" has been going on for months already. You can thank the early/mid November snowfall for that. Since then, we've been on a roller coaster of high and low emotions, with a few head-fakes in regards to the long range pattern. Medium and long range ensemble guidance has not helped in that regard, as they have been too quick to pull the trigger on -EPO/-NAO blocking a few times already in December. The larger scale hemispheric pattern simply hasn't aligned exactly as we have needed it to, and there have been a few misaligned pieces (MJO in particular).
The current upcoming late December period looked quite favorable for a while, but most long range ensemble guidance did a very poor job of resolving the effects of EAMT as well as the MJO. The current MJO amplitude exceeded most ensemble forecast guidance at a 8-14 day lead time. The North Pacific Jet retraction did occur, but we are also seeing a large-scale retrograde of the North Pacific pattern. Without much impetus to prevent this, the Aleutian low will only be present for a day or so before it retrogrades back towards a more unfavorable position and a more notable North-Pacific ridge anomaly develops. This will limit the favorable pattern in the Eastern US quite a bit, and while a gradient pattern may eventually develop, it likely will be largely modulated by a Southeast Ridge that will meet little resistance. The wild card will be the NAO domain, which a negative modality may favor New England late this month for a few events. See the below image -- no bueno. I expect our initial call of a warmer/less snowy than normal December in the Northeast will be correct.
For the most of us, however, this will require more patience and I don't see the late month period to be as favorable as some others at this juncture. The hemisphere is going to reset itself once again. However, I think this requires some larger-scale perspective. Back in early November in our 2018-2019 Winter Forecast we specifically discussed this evolution, with the potential for a briefly favorable period near the holidays. However, it was also discussed ad-nausem that the time frame to watch most carefully was the early to middle part of January. That has not changed, and in fact confidence has probably doubled that this time frame will be extremely favorable.
Most long range model guidance is in agreement on the overall progression of the wave guide. The MJO will continue its progression, coming around the bend and largely expected to weaken. However, the current (Arguable ) - MT state is expected to flip, with the GEFS and ECMWF both in good agreement that the next +MT pulse will begin later this month. EAMT is expected in + territory as we move into the early part of January. Most importantly, for the first time this winter, this will align well with tropical forcing and also aid in the development of a more favorable North Pacific jet.
When you take the sum of these parts and add in the developments in the stratosphere, the true potential breadth and depth fo the situation becomes more apparent. Almost all ensemble guidance is now in good agreement that another notable W1 event will displace and/or split the stratospheric polar vortex, with a complete reversal of zonal winds at 10hPa and the potential for further depth. A subsequent W2 event is not out of the question. In other words, the stratospheric polar vortex is expected to remain extremely weak, perhaps on the periphery of climatology, and the potential exists for a SSW in late December or very early January. While the exact evolution is indeterminate, the percentage chance of a SSW is much higher than normal, and the weakened state of the stratospheric polar vortex significantly enhances the chances for very anomalous high latitude blocking.
I expect the state of the North Pacific to improve dramatically as we move into early and Mid January, and I expect the stratospheric evolution to additionally aid in the development of high latitude blocking. With tropical forcing in a more favorable state, the development of an Aleutian low appears probable. The stratospheric vortex will remain very weakened and supportive of high latitude blocking (-NAM?) - and as a result, I expect a very favorable pattern for colder than normal air and significant winter storms will evolve across the Northeast states by the middle of January, perhaps as early as January 7th and continuing through January 25th. (those dates will need to be amended and honed in)
It is obviously far too early to discuss any specifics, storm threats, intangibles, etc. However, I felt it necessary to touch base on this time period - which currently looks likely to feature the alignment of many features across the hemisphere that we so often struggle to get to work in our favor. My suggestion is to relax and enjoy any snow threats that come prior to that. We are a few weeks away still from this favorable period, but it will be worth the wait and then some.

I have been recently asked to start a thread, to talk about weather teleconnections and similar topics. This is often a topic not very well discussed on other weather places, and places like Twitter. We have a number of experts, enthusiasts, and meteorologists, who are knowledgeable in this area. So this is a thread for technical discussion about the teleconnections, etc, as well as a place for questions about these topics. We need to start talking about these climate drivers more, as they are the key to unlocking medium-long term forecasts. We are making a place for technical discussion about these factors away from the main thread/s. So this thread is born.

Teleconnections that could be up for discussion are: MJO, AAM/GWO, NAO, RRWT, NP jet, Mountain & Frictional Torques, AO/AAO, ENSO, IOD, AMO, SSTs in general, SOI, QBO, the Stratosphere, etc. Feel free to talk about related topics, but stick to this general topic.

I encourage all posters to discuss and pose questions relating to the topic, and keep it a relaxed atmosphere. Any questions, just PM me or comment here.

Since﻿ the service provided through WDT was withdrawn there was a gap in this vitally important data. I've been in touch with Ed Berry, who along with Dr Klaus Weickmann (who retired 2 years ago) developed the GSDM (I posted on that on both the 33 and NetWx forums with Ed's excellent presentation earlier this year) and he told me that a friend of his still processes this data. He has kindly provided a link to that site plus the access user name and password:﻿

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To get the ball rolling, I should mention the MJO's return to strength soon, into P7&8. EPS and GEFS have similar forecasts, with the GEFS downgrading the MJO strength over the past few runs.

It has been interesting to watch guidance trend a bit back to the base state we saw earlier in the winter months. The higher latitudes have reshuffled a bit and we are losing support for +anom heights in the mid level higher latitude atlantic domain. At the same time we are seeing a bit of a retrogression with anomalous ridging developing in the Pacific once again.

This will serve to dislodge very anomalous cold southward into Canada and the Northern 1/3 - but the longevity of it becomes the most interesting thing to me. It seems to me there are *early* signals for big time warmth toward the end of April and possibly even early May with the overall progression of tropical forcing/convection and higher latitude pattern. Some of the details are still yet to be determined, but we will obviously discuss at length here in this thread as we move forward!

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It has been interesting to watch guidance trend a bit back to the base state we saw earlier in the winter months. The higher latitudes have reshuffled a bit and we are losing support for +anom heights in the mid level higher latitude atlantic domain. At the same time we are seeing a bit of a retrogression with anomalous ridging developing in the Pacific once again.

This will serve to dislodge very anomalous cold southward into Canada and the Northern 1/3 - but the longevity of it becomes the most interesting thing to me. It seems to me there are *early* signals for big time warmth toward the end of April and possibly even early May with the overall progression of tropical forcing/convection and higher latitude pattern. Some of the details are still yet to be determined, but we will obviously discuss at length here in this thread as we move forward!

Yes, I can certainly agree with all of that. Glad to see you here @earthlight

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I'd say I at least know the general concepts and the causes/effects of most of these variable teleconnections except Angular Momentum and Frictional/Mountain Torque. Could someone kindly direct me to a place to read up on these concepts?

Also, to any of the more knowledgeable people here, with the oncoming solar minimum from cycle 24, what are the potential effects to the global teleconnections?

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I'd say I at least know the general concepts and the causes/effects of most of these variable teleconnections except Angular Momentum and Frictional/Mountain Torque. Could someone kindly direct me to a place to read up on these concepts?

Also, to any of the more knowledgeable people here, with the oncoming solar minimum from cycle 24, what are the potential effects to the global teleconnections?

This is the formal paper from Klaus Weickmann, who was one of the leaders in early GWO research.

Basically Frictional Torque is the tropical component, and the mountain torque is the extratropical component, togther they form the AAM. The MJO can also be used to indicate the AAM, with Phases 5-8 more associated with positive AAM and Phases 1-4 with negative AAM. But this isn't always the case, so you have to look at the torques as well.

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@Snowy Hibbo fascinating article - many of these teleconnections are not complex - but they are not completely understood in the hobbyist community.

Cheers to this thread, and hoping we can all learn a bit. We realize in some places, these connections have been discussed at great length. Thanks for bringing that to 33. Looking forward to growth and learning in our international group!

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Hello everyone, this is a great idea for a specialist thread on this forum Zac ( @Snowy Hibbo) and a great introduction to get it all going.

This is my first post on this forum. I'm not quite sure how I've been given such an elevated status of "Master Wx Expert" as I only enrolled on here a week ago I do post regularly on a UK forum and that's where Zac and I started exchanging PMs. I run a full time online business (not weather related) and often struggle to find time to embrace this wonderful subject as much as I would like to. Although many of my posts are slanted towards the UK and Europe, I do also focus on the broader patterns, the drivers and what's behind the model output. Quite recently I have been learning about atmospheric angular momentum (AAM) and the torques. I consider myself very much a learner but I like to write up my current thoughts to set them straight and I am always grateful for corrections and comments - surely the best way to learn? I also love to participate in debates. I will make a real effort to support this thread. Sometimes I will cross-post my UK reports (or parts of them) onto here when I feel that they are relevant. I will also write a few posts specifically for this thread. I'm pretty tied up until after the Easter holiday period but I'll kick things off with a little bit on AAM.

There's a small group off us (in the UK) who have been looking for decent up-to-date AAM data. Since those two NOAA scientists (Dr Ed Berry and Dr Klaus Weickmann) retired a couple of years ago and took their GSDM (global synoptic dynamic model) copyrights with them, they and their work have never been replaced. Very recently Zac told me about a brand new educational site being set up by Dr Victor Gensini (of the NIU, Dept of Geographic & Atmospheric Sciences). Here's the link: http://atlas.niu.edu/gwo/ This site is still under construction and evolving but it already contains some excellent data on AAM and the GWO (global wind oscillation). Here are some current charts:

The first thing to note is that there has been a known permanent negative bias in the GEFS AAM forecasts. Victor's chart is "bias corrected" which is really useful.

Victor also shows CFS data, something that we couldn't previously get access to in the UK on any "free-to-view" sites.

He also shows GWO plots for each CFS ensemble member - I have only posted the mean chart with all four members. So a much smaller number of members compared to GEFS but very useful to have data from two different models. Here's a current GEFS GWO chart for comparison from the Nicholas Schiraldi Albany site + a link): http://www.atmos.albany.edu/student/nschiral/gwo.html This shows up the negative bias very well (compare the values to the top chart).

The GWO is a measure of AAM, plotting it in its various phases. It's always useful to view this excellent annotated chart:

Victor plans to add torque forecast charts to his site very soon. We have not seen these (in the UK) since the GSDM was discontinued. For now, we make do with these charts which are usually several days behind:

Frictional Torque (FT)

Mountain Torque (MT)

There have been some interesting recent changes. AAM (see another of Victor's charts below) spiked from negative to around neutral from early to mid March, before dipping again slightly in the last couple of days. The fairly modest uptick in AAM (GEFS bias adjusted chart and the CFS charts) and both FT and MT going positive may be just what the tropospheric patterns need to help off-set the remaining SSW (sudden stratospheric warming) imprint or signature on the northern hemisphere. Are we finally seeing the demise of La Nina? It has been weakening steadily and the NOAA prediction up until their last weekly report on March 19th (update due later today/tomorrow) was for a 55% chance of a return to ENSO (El Nino Southern Oscillation) neutral conditions in March to May and then remaining neutral for the rest of 2018. The MJO is also just coming to life again (as Zac and several others have already referred to) with decent amplitude in phases 7, 8 (and perhaps 1 indicated) may be assisting further HLB for a while longer. Although it's far too early to say, I would agree with several views that we may see a strong warm up in mid to late April. Before then, particularly in Europe and may be the UK, we may see further bouts of some pretty cold conditions. We may go from cold to warm in a matter of days in around 3 to 4 weeks time. We need to keep an eye on the ENSO state (La Nina might strengthen again) as well as the other drivers to ensure that the very recent trends continue and we're on track.

I'm really running out of time now, so I'll copy a small section from a recent post of mine (on the UK forum) which I've edited slightly. This might help those learning about AAM and the torques (please remember that I'm still learning myself). This outlined the AAM phases and timing in late January and early February 2018 that assisted with the SSW impacts:

...."Looking at the chart above with the AAM anomaly for the last 90 days (these charts are available to go back over a full year) we can clearly see the spike from the low point mid January until the high point in early February that I referred to as the chain of events that helped to trigger the SSW (or at least its final impact on the surface as the processes had already been initiated). You can see the spike in the torques which occurred during February.Quite a few people get confused by the timing and impacts of these processes,as did I until a few months ago. If you refer to the annotated GWO phase chart you can see thatthe process actually starts when AAM spikes from a negative or even a strongly negative position not just when it has gone positive. So in mid January AAM was shown as close to -3 with east Indian Ocean "maritime convection" or around GWO phase 3. Then the chain of events begins. As AAM rises into phase 4 (still negative) FT starts to rise. Then as AAM continues to rise it usually starts to become positive (towards the GWO phase 5) and this is when MT starts to rise. This chain of events has a usual time lag of around 10 to 14 days (in this case from just after mid January to very early in February). The different colour lines on the lower section of the MT chart represent the different torques (the key to these is immediately above that lower section). The black line represents the global torque which was strongly positive for a short while. With this phase of positive MT it was the EAMT (East Asian Mountain Torque) that was the main northern hemisphere influence. As this energy forcing circumvented the globe (known as Rossby Waves which also impact on the jet stream causing it to meander) it interacted with the Himalaya mountain range. This sent up energy waves high into the atmosphere, through the troposphere and into the lower stratosphere. This involved a further time lag. Other factors in the strat were already initiating the earlier stages of the warming. Think of the MT energy waves as giving the process a violent nudge. Sometimes warming events do not propagate effectively down to the surface layers. The MT forcing was probably "one" of the key contributory factors in "triggering the final stages" of the SSW and its impact on the surface. These processes and interactions are only beginning to be understood. AAM probably always plays its part in this process. It is not always EAMT that has the largest impact on the strat. Sometimes it is NAMT (North American Mountain Torque over the Rockies) but not on this occasion (it had been positive in January but was slightly negative during the key period in early February). There have been a few papers on the impacts of MTs on the strat in relation to earlier SSW events. The term is also known more generally as "orographic forcing".

My outline of the AAM processes above is probably over simplified and I still have a lot to learn about stratospheriic weather, warmings and SSWs. One thing that I would like participate in after Easter is a thorough post mortem and debate into the causes, timing, triggering and impacts of the SSW, This will include an examination of past MT forcing types and the links with previous SSW events. It will also be fascinating to see when previous potential SSWs came close but failed to reach the surface. I'm wondering if there was little or no AAM/FT/MT assistance in these years. This should also give us all a better idea of the degree of AAM influence and whether or not it must be an essential ingredient to the overall process. This debate will go ahead on the UK forum but I feel that a similar debate can take place on this thread. I will be happy to cross post and contribute to both threads on this. There are a number of past papers on AAM (and particularly positive MT) and the influences on the lower stratosphere. There is a lot of material to cover and surely all of us who are interested can learn more from this year's SSW.

It may well be next week before I can manage a full post again but I'll check in on here regularly. David

EDIT: I see that Tamara has just done an excellent post below mine which is a far better and more thorough explanation of the AAM processes than I managed. Tamara has actually assisted me greatly in learning all about AAM and I'm very grateful for her being so patient with me. These days, new concepts take a while to sink into the grey matter!

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A 'hello' from me as one of the new member little group that @Snowy Hibbowas kind enough to introduce Thanks to him for starting this excellent and highly valuable thread which should provide an abundance of new information for everyone - and will I am sure cater for all the different individual learning curves of various members.

A few years back I was struck by how the Global Synoptic Dynamical Model (GSDM) could be used as a heads-up assist to gauging future weather patterns and decided to do some quiet self study combining outside reading with some existing practice work from expert meteorologists already hooked by the concept ideas of this model.

There have already been some great posts on this thread and I hope that my own offering here avoids too much duplication and can be of some help to the discussion

The Global Wind Oscillation is a plot depicted measurement of net total global wind-flows aggregated through tropical momentum transport energies - constantly fluxed and exchanged between the tropics and extra tropics by changes in atmospheric angular momentum (AAM). These dynamic processes effectively provide good markers as to how the global jet stream might behave - AAM itself is a measure in simple terms of the turning force of the Jetstream (through frictional and mountain torques).

The GWO is depicted by a phase plot spider graph (below) which reflects whether the global atmosphere is pre-disposed towards easterly wind additions (La Nina-like) or westerly wind additions (El Nino-like). There are eight phases in total. Three La Nina attractor phases 1,2 and 3. Three El Nino attractor phases 5,6 and 7. And two 'transitional' phases 4 and 8. The former transitional phase 4 depicts rising AAM in a La Nina state (or westerlies being added to an easterly trade wind dominated state) and the latter phase 8 depicts falling AAM within an El Nino atmospheric state or (easterly trades being added to an atmospheric state that has greater overall westerly wind inertia within it).

See below a basic template of this next to a live plot depiction of the atmospheric state in action. The tropical (MJO) and extra tropical (GWO) elements of the atmospheric circulation are reflected within the contents of this template and an introduction of how momentum transport within the tropics is processed in the extra tropics through a programme of frictional and mountain torque mechanisms. For purposes of this post I am not going to discuss the latest position wrt GWO - keeping it informative rather than any forecasting element

The hard part, is gauging in the future how anticipated tropical convection patterns will evolve those wind-flows in the extra tropics, as rossby wave trains (which are triggered by the windflows created ahead of tropical thunderstorm activity) propagate eastward and northwards into the extra tropics. The initial consequence of an event in the tropics is a frictional torque at the ocean surface, and depending on the strength of the resultant rossby wave, this can propagate polewards and set up the mountain torque in the extra tropics. These mountain torque processes in turn have implications for the tropospheric/stratospheric relationship - and the relative strength/weakness and organisation/disorganisation of the seasonal polar vortex.

So getting right to that hard part. Tropical convection with its associated wind-flow additions and torque mechanisms is an expression of change to atmospheric angular momentum. As indicated above, AAM is quite literally referring to the turning force exhibited on the jet stream. That makes sense when you think of convergence and outflow wind mechanisms that are associated with convection events even on a minor micro-scale level with local thunderstorm development. Extrapolate that much larger with MJO convection and you get a large scale forcing across the tropics with the linear bands of convection that occur with the cyclical timelines of this phenomena.

So, that means westerly wind burst additions (WWB) are added across the tropics associated with the MJO as it heads eastwards from the western hemisphere. Westerly winds create a +ve frictional torque (convergent) which can under suitable conditions propagate with sufficient strength into a +ve mountain torque 'event'. The turning force in this case is of westerly winds hitting a tall mountain range (such as the Himalayas or Rockies), deflecting wave activity upwards into the stratosphere

All good so far.

However, Mother Nature abhors a vacuum - and where westerly winds are added, there has to be a compensation elsewhere in the atmosphere with easterly winds to fill the inertia vacuum

This compensation process of wind-flow exchange to maintain atmospheric parity is referred to in the GSDM as the 'AAM budget'.

This post cannot cover the whole science in fell swoop, but lets take a look at some of the main elements of the GWO budget. The descriptors below are not all of the categories that comprise the whole AAM budget - but are main contributors that make up the global jet stream (as NWP drivers) and having some understanding of these is a solid introduction to the GSDM

Calculated AAM tendency:

This plot depicts the net total global wind-flows calculated from frictional and mountain torques in the tropics and extra tropics. In other words a useful guide to the net budget of tropical momentum process (as discussed above). If calculated tendency is -ve, then this tells you that net global wind-flows as calculated by torque forcing have greater easterly (La Nina-like) inertia to AAM budgets. The converse iS true if calculated tendency is +ve - suggesting that westerly winds are being added to global wind-flows through +ve torque mechanisms via tropics>extra tropics

Relative AAM tendency:

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This is an indicator of the direction of travel of angular momentum relative to GLAAM . If tendency is sharply down as indicated on the latest plot for example, this suggests that at the given time large amounts of easterlies are being added to the atmosphere through -ve torque processes - and relative to total AAM, will likely pull GLAAM further downwards. Again the converse is true for +ve torque processes. So this means that atmospheric angular momentum tendency is a refection of the size of the frictional torque created by MJO activity in the tropics (see above for frictional torque definition and plot)

Total Atmospheric Angular Momentum: . .

Essentially already explained. - This plot depicts the measure of the total global wind-flows (westerly and easterly) that the atmospheric circulation has the capacity to hold at a given time. Its the bell-weather indicator for the ENSO ocean>atmosphere relationship and calculates the net total wind-flows globally (easterly or westerly as the case maybe) after both calculated tendency and relative tendency have been included. However, as indicated above, total AAM is set against the trend direction of atmospheric feedback which is measured by relative AAM tendency.

Clearly, the ENSO state is a large scale governor of total AAM as defined by La Nina or El Nino and the extent of the total forcing that SST feedbacks have on the behaviour of MJO and other forms of tropical convection such as cyclones or typhoons (depending on which part of the world they occur)

On that basis, modelling of the MJO is notoriously tricky, and prone to error beyond, say, especially 5 days out. That is before attempting to gauge the extra-tropical (GWO) response in terms of net total windlfows that will be a consequence of any MJO event. With La Nina present for some time (and only now waning) its always been logically intuitive to expect there to be a surfeit of easterly wind inertia in the mix - a natural product of the stronger trade winds which occur under a Nina

Synoptically, a surfeit of easterly winds in the atmospheric circulation system will be represented by divergent (stable) patterns across the ENSO zones. This leads to a build of the circum-global ferrel cell sub tropical anticyclones - stemming initially from the tropics > into the Pacific and then extending around the globe as part of a typical long-wave pattern. These anticyclones dictate patterns at Northern Hemisphere mid latitudes, whilst at higher latitudes the pattern is controlled by the strength of the seasonal polar vortex in winter-time. So its easy to see how increased polar jet flow occurs above these sub tropical highs, whilst underpinning beneath them the -AAM tropical easterly trade winds

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The amount of easterlies added in the tropics will naturally determine the extent that westerly wind additions can be made through tropical convection. If you think of easterly wind shear buffering up against tropical convection, then its not hard to visualise how the WWB's are 'sheared off' and neutralised. This, effectively kills off the forcing of the MJO activity and hence under La Nina conditions its easy to see why easterly wind inertia commonly inhibits activity the further east one heads from the western hemisphere.

The departed winter season so far however has been a-typical in terms of the SST distribution of the La Nina across the Pacific. There have been reasonably warm anomalies in the western most Pacific plus the areas of ocean of the Gold Coast, and towards Indonesia than often is the case in a traditional La Nina event. This means a Nina atmosphere/ocean disconnect has been attempted through the winter, culminating in the massive tropical momentum event propagating from tropics>extra tropics>SSW.

To conclude this long post, I am including a technical link that describes the processes of the GSDM (Global Synoptic Dynamical Model)

The post is already way too long (!) so no to attempt to go into detail of its contents, but maybe some are brave enough to try to read through it. Its bound to create some difficulties, but it is a large part of what I have tried to wade through in the last couple of years to try and get some further insight into this fascinating but not widely known concept model of atmospheric dynamics. It was put together by Klaus Weickmann and Ed Berry, two officers from noaa who have subsequently retired and taken the official links at NOAA away with them. I think these guys have left an incredible legacy that folk of all different meteorological levels should support in their learning and in turn put forward as an integral part of their forecasting aims.

The GSDM surely provides an essential insight into the complexities of trying to forecast and anticipate the evolution of medium and longer range NWP.

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Hi Everyone. Great to be joining 33andrain and I’ll start by thanking @Snowy Hibbo for inviting me to join. Looks like you guys have a great forum going on!

A life-long weather enthusiast my more recent interest is the stratosphere and I’d like to take a quick look at how fall-out from the Feb 2018 Sudden Stratospheric Warming (SSW) is continuing to influence the USA weather in the short-term.

To set the scene a quick look at how the stratospheric polar vortex (SPV) is doing. After the SSW of Feb 12th the zonal mean zonal winds at 10hPa 60N recovered to a weak westerly. A second but lessor SSW occurred on Mar 20th. At one stage this was thought to be a possible final warming before the SPV dissipates for the summer, but a further weak recovery occurred. It’s now looking like the final warming is likely to take place around April 11th.

So the SPV remains weak and split, with a lobe over Siberia but another lobe located over Alaska/British Columbia. The stratosphere and troposphere are currently still reasonably well coupled as can be seen from the geopotential height anomaly charts for 10hPa, 50hPa, 100hPa and 500hPa and then the 500hPa pressure chart. The resultant pattern on the ground suggests a delay to Spring with cold air and further snow impacting the northern States of the US in early April.

Anomaly charts for T180 (April 3rd) 10hPa, 50hPa, 100hPa and 500hPa.

500hPa pressure chart:

The SPV charts above only go out to April 3rd, but if we move on a few days (to April 7th) and look at the 850hPa temp anomaly, 2m temps and precipitation charts (hatched is snow) it confirms the ongoing influence of the vortex on northern (and mid?) States with current forecasts showing the potential for significant frontal snow moving south:

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Guys - sorry to say the website hosting the stratosphere 10hPa, 50hPa and 100hPa charts used in my post (above) is having technical problems at the moment, so the charts currently aren't displaying. Hopefully they'll be back soon as they show the coupling between strat and trop and show how the split vortex continues to impact. In the meantime Michael Ventrice has just tweeted this chart which draws the same conclusion for start of April.